Automobile headlights wherein a replaceable lamp unit is employed are known in the art. Examples are illustrated in U.S. Pat. Nos. 3,688,103 (Daumuller), 3,593,017 (Cibie) and 2,750,491 (Anderson).
As stated, the instant invention is related to lamps of the variety described above and in particular defines a method of making a replaceable lamp unit which provides both a hermetic seal for the unit within the headlight's reflector and also assures that the electric lamp utilized therewith will be maintained in strict alignment as is necessary in automotive headlights. By the term hermetic seal is meant a seal which prevents the passage of moisture, dust and other elements which can adversely affect the operation of the headlight. By way of example, excessive moisture entering the headlight can adversely affect the reflective coating typically utilized on the concave reflector of the headlight, and thus significantly reduce light output.
In addition to providing a hermetic seal, the replaceable lamp unit defined herein assures that alignment of the electric lamp employed therewith will be maintained. That is, alignment of the glass envelope of the lamp relative to the unit's holder is provided such that the filament structure therein (either a singular coiled filament or two, spaced coiled filaments) will be accurately aligned relative to the optical axis of the reflector when the lamp unit is oriented within the reflector's rear opening.
As also described herein, a preferred light source which constitutes an important part of the replaceable lamp unit defined herein is an electric lamp of the tungsten halogen variety. One example is shown in U.S. Pat. No. 3,829,729 (Westlund, Jr. et al), said patent assigned the same assignee as the instant invention. In tungsten halogen lamps, the tungsten which constitutes the filament material is normally evaporated from the filament during lamp operation and combines with the halogen to form a gaseous halide, said halide preventing the tungsten from depositing on the internal wall of the lamp's glass envelope. Upon returning to the filament structure, the halide decomposes, resulting in the deposition of tungsten back onto the filament structure and the release of additional halogen gas to assure continuation of the cycle. The halogen cycle is well known in the art, and lamps employing it have been used for some time. In the case of the two beam (dual filament) lamp, a typical tungsten halogen lamp provides about 65 watts when operated at high beam and about 35 watts at low beam. Understandably, it is critical that the filament structure of the lamp within an automobile headlight be aligned relative to the reflector to provide optimum output of the finished headlight. As will be described below, such alignment constitutes an important feature of the replaceable lamp unit defined herein.